Hong Kong officials have faced criticism over their handling of the discovery of a banned substance in the water supply of two public housing estates, as lawmakers and experts accuse the administration of being slow to respond, failing to show accountability and lacking awareness.

A veteran political analyst also called the government’s response “embarrassing”, saying it undermined the city’s efforts to show improvements in public welfare before an anticipated visit by a senior Beijing official.

Seven days after the case of bitumen in the water supply came to light, Chief Executive John Lee Ka-chiu on Friday night listed out 10 response measures for government departments to implement. The moves include setting up an expert team to trace the source of the substance and replacing the water pipes involved.

But the government has yet to fully explain the presence of bitumen – a petroleum-derived substance banned from use for pipes after 2005 – in drinking water at Queens Hill Estate and Shan Lai Court in Fanling. Residents first reported finding “mysterious dark substances” on Friday last week.

“The incident shows two major flaws of the government,” said Sonny Lo Shiu-hing, a veteran political commentator and observer of the politics of Hong Kong and Macau.

“It was slow in response and it failed to name the cause, thus it was unable to provide accountability.”